Combining experts from the medical and materials sciences, the Institute considered current concepts in medical and materials sciences as they relate to implantable prostheses in orthopedic surgical practice. The syllabus included theory and applications of materials properties, physiological function, and host response to metal and non-metal materials. Total hip prostheses are the most common orthopedic device implanted today involved in over 200,000 operations. Failures occur at the rate of 10~-40~ at ~ to 10 years. Failures are due to loosening, infection, fracture of femoral components, or destruction of the pe 1 vi c components .' All these, and other problems related to the implantation of the devices, the surgical procedures, and device pathology, were. discussed in light of current, as well as, emerging technologies and scientific knowledge. Repeatedly, scientists designing prostheses became aware of a lack of understanding of physiological phenomena associated with biocompatibility; the interchange among practising physicians, basic scientists, and pathologists at this Institute was appreciated. We thank all the contributors and participants for their effort. Thanks are also due to the personnel of the Scientific Affairs Division of NATO. The daily routines of running the Institute were greatly facilitated by the efforts of Pedro Cuevas, M.D, Jose Gutierrez Diaz, M.D, and Dr. Hanita Kossowsky. The devoted help of Nir Kossovsky, M.D, in setting the conference and in editing this book, is sincerely appreci ated.